Factor XIII in the treatment of hemophilia A.

n engl j med 366;3 nejm.org january 19, 2012 281 not match that of the patient. Tiede et al.2 observed that some patients with acquired hemophilia have been exposed to a factor VIII protein that does not match their own. Specifically, there are polymorphisms of factor VIII at amino acids 1241 (Asp→Glu) and 2004 (Glu→Lys). In patients with certain HLA-DRB1 alleles, exposure to a “foreign” factor VIII variant protein may result in a major-histocompatibility-complex class II presentation of novel T-cell epitopes. It was not clear whether the patient had been transfused before hemophilia A developed. It would be interesting to know whether the patient was transfused before ipilimumab therapy and thereby possibly exposed to a foreign factor VIII protein.